Measuring the electric potential or the electric field strength on the skin of a person by means of electrocardiographic sensors forms the basis for many medical diagnostic methods. By way of example, this allows an electrocardiogram (EKG) to be recorded or the heart rate to be established from the measured electric potentials.
In conventional methods for measuring the electric potential on the skin, said electric potential is registered by electrodes which are in direct electric contact with the skin surface. Thus, an electrically conductive connection between the skin and the electrode is established. However, it is found often to be difficult to ensure a sufficiently good electric contact between the electrode and the skin, and hence the body of the person to be examined. Moreover, the use of such diagnostic methods is increasingly also envisaged in fields of application in which there is no direct access to the skin of the person to be examined, such as e.g. in vehicle applications for monitoring bodily functions and/or vital parameters of vehicle occupants on seats or couches.
Thus, for example, U.S. Pat. No. 7,684,854 B2 discloses a sensor for a contactless electrocardiographic measurement on a person. In this case, the person can be situated on a chair, in a bed or on a vehicle seat. The electrocardiogram can be recorded from the body of the person wearing clothes, without direct contact to the skin. The sensor comprises an electrically conductive, substantially flat electrode, which has a measurement area facing the person and a connection area facing away from the person and lying opposite to the measurement area, which connection area is electrically connected to a preamplifier. The electrode and the preamplifier of the sensor are surrounded by a shield.
A further contactless sensor for recording an electrocardiogram of a person is disclosed in EP 2 532 306 A1. The sensor comprises an electrically conductive electrode and a detection apparatus, which is electrically connected to the electrode and configured to amplify the signals recorded by the electrode. The sensor is provided to be arranged in a vehicle seat and to establish certain physiological parameters of a driver sitting in the vehicle seat.
DE 20 2012 001 096 U1 discloses capacitive sensors for registering vital parameters of a driver of a vehicle. To this end, the sensors are attached in, or on, the back of the seat of the vehicle. In particular, in accordance with one embodiment, it is proposed to arrange the sensors in, or on, the back of the seat in two rows separated from one another by a distance corresponding to the width of the spinal column of the driver. In each row, the sensors with an area of 16 to 36 cm2 are arranged at equal distances of 1 to 5 cm from one another. In a further embodiment, two film sensors with a width of between 4 and 10 cm, separated from one another with a distance corresponding to the spinal column, are arranged over the whole height of the seat instead of the two sensor rows, separated from one another, with sensors distributed over the whole height of the seat at a distance of 1-5 cm.
Furthermore, DE 10 2008 049 112 A1 discloses a capacitive textile electrode for measuring bodily functions and/or vital parameters of persons for vehicle applications, for example in a seat or a couch, which electrode has a multi-layered design. The latter comprises two textile layers, which each have an electrically conductive electrode region, wherein a further textile layer is provided for establishing a distance between the two other textile layers.
In order to obtain a reliable and stable signal from the known sensors or sensor arrangements/arrays for a contactless electrocardiographic measurement on persons in vehicle applications, it is essential that the sensors are covered, at best completely, by the body or the body region to be examined of the person, and that a distance which is as small as possible is ensured between the sensors and the person to be examined. In general, those electrodes which have a large distance, e.g. to the back of the person to be examined, lead to a poor or even unusable signal.
Therefore, in principle, attempts can be made to place the sensors e.g. on a seat or couch area where a contact, which is as good as possible, is to be expected between the person situated in the seat or on the couch and the seat or the couch. However, in the case of relatively slim persons—due to their low weight—or in the case of persons which have an anatomical deformation such as e.g. lumbar hyperlordosis, it will be relatively difficult to ensure a sufficiently high contact pressure and a sufficiently large contact area between the measurement area of the electrode and the person to be examined. It follows that, particularly in the case of such persons, the probability of low quality measurement signals recorded by the electrode will increase.